Ball latch mechanisms are typically used for releasably engaging one member to another. Such mechanisms typically include an outer tubular member, an inner cylindrical member and a cage member concentrically located between the outer and inner member, the cage member having a plurality of circumferentially arranged apertures for receiving spherical balls. A cylindrical inner wall of the tubular member has grooves that may be aligned with the apertures of the cage member for receiving the spherical balls. Similarly, an outer wall of the cylindrical member has notches for receiving the spherical balls. In a latched condition, the balls are simultaneously disposed in the apertures of the cage member and the grooves of the outer tubular member, preventing any relative axial movement between the two. To unlatch the tubular member from the cage member, the inner cylinder member is moved, either rotationally or axially, relative to the cage member such that the notches of the cylindrical member are aligned with the balls. In this position, the balls are permitted to retract radially below the outer surface of the cage member into the notches and the tubular member is free to move axially past the balls.
In some situations, it may be desirable to apply a large axial load to the outer tubular member in the latched condition which, upon unlatching, causes an immediate and powerful axial movement of the outer tubular member with respect to the cage member. One application for such a device would be a preloaded impact member that is used to strike an object with a high impact force. In such a case, the inner tubular member would act as a trigger for releasing the impact member. A difficulty encountered in this application, however, is that the axial load applied to the impact member in the latched condition would be transferred through the spherical balls to the cylindrical member. Thus, a relatively high force would be required to overcome the high frictional forces between the spherical balls and the outer wall of the cylindrical member in order to align the notches of the cylindrical member with the balls, releasing the impact member.
It will be appreciated that a disadvantage of the ball latch mechanism mentioned above, especially in the context of a trigger mechanism, is that a larger, more powerful, device is required to reliably effect the necessary movement of the cylindrical member to move the balls to the unlatched position. Accordingly, there is a need for a ball latch mechanism that effects movement of the trigger using only a relatively low force, yet is nevertheless adequate to latch and unlatch a highly loaded impact member. The present invention satisfies this need.